The present invention relates generally to plasma processing chambers, and more particularly, to systems, methods and apparatus for accurately detecting the actual DC bias on a substrate being processed.
Plasma processing is very common in manufacturing semiconductors. Plasma processing is typically a plasma etch process where plasma ions produced in the plasma react with an exposed layer of the substrate. The depth the plasma ions can penetrate into the exposed layer of the substrate is determined by the energy of the plasma ions. The energy of the plasma ions is at least partially related to the bias applied to the substrate.
Ever higher aspect ratios of depth/width are sought as semiconductor device sizes become smaller and more densely packed. The higher aspect ratios require plasma ions with an increased energy level.
One approach to increasing the energy of the plasma ions is to increase the bias voltage. Unfortunately, as the bias voltage increases, arcing occurs between the substrate and the processing chamber and between the electrodes and the processing chamber structures. Further, even relatively small intrusions into the biased region of the substrate or the plasma electromagnetic field can cause significant disruption of the respective electrical fields and thus cause localized plasma ion energy fluctuations. Thus resulting in localized non-uniformities in the plasma etch process.
The typical method and structure used to detect the DC bias of the substrate is a contact pin. However, the contact pin disrupts the electromagnetic field of the substrate or the plasma electromagnetic field. Also, as the bias levels increase, arcing can occur between the substrate and the contact pin. This arcing can damage the contact pin and distort the detected level of the actual DC bias present.
In view of the foregoing, there is a need for a system, method and apparatus for more accurately measuring the DC bias without causing corresponding, localized non-uniformities in the plasma etch process.